They wouldn't necessarily use all the doubles at once. Given that a SalemDay lasts anywhere from 4 to 12 episodes, anything is possible. Besides, someone can't go delusional overnight. A week in Salem can span 20-30 episodes, especially during sweeps, which generally end up being 2-3 extra-long SalemDays.

Plus, they may have filmed plenty of ED scenes to drop in for weeks. That's what they did with Molly and PR.

I would love to see it all be part of a Stefano plot, but I don't get the impression that this current regime wants a return to the Years of Dr Rolf, with implanted memories and diabolical (and ultimately nonsensical) plots involving dopplegangers. Stefano has transitioned from criminal kingpin to maniacal Marlena obssessive to grandfatherly to aging horny businessman.